Habitual marijuana consumers may start to lose control over their muscles and develop symptoms of several muscle disorders, according to new findings from a team of Spanish researchers.

Modern scientific research has determined that use of the plant-based drug marijuana/cannabis can significantly impair a person’s ability to properly coordinate the use of his or her muscles. In a study scheduled for publication in May 2015 in the journal Neuropharmacology, researchers from Spain’s University of Cadiz explored the impact that any given session of cannabis use can have on the basic muscle function of a habitual consumer of the drug. These researchers concluded that marijuana/cannabis consumption is linked to muscle cell dysfunction and increased risks for symptoms of muscle disorders such as dysarthria and ataxia.

Marijuana and Short-Term Muscle Coordination

Marijuana/cannabis produces its primary drug effects when its main ingredient, THC (tetrahydrocannabinol) reaches the brain after passing through nerve cell sites called cannabinoid receptors. THC is perhaps most noted for its ability to trigger feelings of euphoria in a part of the brain called the pleasure center. However, the chemical also produces changes in other parts of the brain, including the areas responsible for coordinating muscle movements and giving humans the ability perform complex or intricate physical tasks. Scientists commonly refer to this muscle coordination ability as psychomotor muscle control and distinguish it from basic control of individual muscles.

Loss of psychomotor control can substantially alter the functional state of someone under the influence of marijuana/cannabis. For instance, lack of muscle coordination can seriously impair a marijuana/cannabis consumer’s ability safely operate a car or any other type of motor vehicle. This is especially true because people under the influence of the drug also commonly experience a decline in their ability to think clearly and exercise sound judgment. Impaired driving risks rise even higher in a marijuana/cannabis user who also consumes alcohol, another substance capable of mildly, moderately or severely degrading muscle coordination and judgment skills.

Muscle Disorders

A person affected by the muscle disorder called ataxia experiences medically significant muscle coordination problems. Potential manifestations of these problems include loss or degradation of fine muscle control, loss of control over eye movements, unstable body posture, an inability to speak without slurring words and an impaired ability swallow normally. A person affected by dysarthria loses at least some of the ability to control the muscles required for speech (e.g., the tongue, the diaphragm and/or the lips). Potential indications of the condition include loss of normal lip or tongue agility, mumbling or slurring while speaking and speaking unusually slowly or rapidly.

Marijuana and Degraded Muscle Control

In the study published in Neuropharmacology, the University of Cadiz researchers looked at the impact that THC and other marijuana/cannabis ingredients have on the health of the nerve cells responsible for controlling the body’s muscles. This level of muscle function is essential for the coordination required for complex movement and reflects the body’s core ability to work properly. The researchers specifically focused on the impact that marijuana/cannabis has on the normal ability to use the tongue, which plays an essential role in functions that include the ability to eat, the ability to speak and the ability to breathe.

In laboratory testing on animals, the researchers assessed the effect of marijuana/cannabis exposure on the tongue muscles’ individual nerve cells. They concluded that the presence of THC and other ingredients can effectively slow down the rate of communication between these cells; in turn, a diminished rate of communication in the tongue’s nerve cells can contribute to significant weakness in the muscle. In a person who habitually consumes marijuana or other forms of cannabis, any specific instance of use could potentially lead to symptoms of dysarthria, as well as short-term symptoms of ataxia and generally poor muscle coordination.

The study’s authors believe their findings may help explain why some habitual marijuana users (many of whom are addicted to the drug and meet the terms used to diagnose cannabis use disorder) develop speech impairments or swallowing or breathing difficulties, or otherwise appear to lose some of their ability to control their basic muscle functions. The authors also believe that they are the first researchers to go beyond cannabis-related problems with higher-level muscle coordination and focus on the drug’s more basic muscle-related impact.